This invention relates to casting dies formed of high temperature resistant, low coefficient of heat expansion materials such as graphite, and in particular relates to an improved two-piece die construction. Such dies are used in conjunction with casting devices which direct molten metal especially previous metals such as gold and silver into an entrance cavity as provided in such dies. The opposite or exit end of the die is cooled, as by contact with circulating water, so that the molten metal entering the cavity solidifies therein and may be continuously withdrawn from the exit end in the form of strip or bar stock. Since graphite is resistant to high temperatures, has a low coefficient of heat expansion and is relatively inexpensive, it is commonly used in the construction of such dies.
The prior known graphite die has generally been formed of a one piece construction and includes a longitudinally oriented internal die cavity most often formed by time-consuming boring operations. These operations not only add to the expense of such dies, but further necessarily result in cross-sectional die cavity configurations which are rounded at the corners thereof. Such rounded shape is imparted to the strip or bar stock produced by such die and upon subsequent rolling and other forming operations has been found to contribute to edge cracking.
It has been attempted on numerous prior occasions to produce segmented or two-piece die constructions in which the die cavity or slot was machined as by inexpensive milling procedures in one or both of the die segments, which in the use thereof are held in face-to-face relationship to form the overall die construction. Dies so constructed, although utilized, generally involve either overly complex methods to hold the segments together during use, or are subject to separation during use. If the segments separate, the molten metal confined within the forming cavity may flow, i.e., flash, into such separation and after solidification form a fin which will hang up in the die and force a shutdown of the casting operation. In this regard it should be pointed out that the casting operation depends on the continual movement of metal in fluid form into the cavity and subsequent withdrawal thereof in solid form from the bottom thereof and any extensions from the solid metal column would prevent this.
One procedure utilized to hold segmented die portions together has been glueing, wherein the die segments are held under high pressure in face-to-face relationship during the curing of the adhesive. Such procedure is, as above indicated, not only expensive but has been found to lead to erosion of the adhesive interface during the casting procedure, which as with the separation of the die segments themselves is apt to form an opening into which molten metal may flow, subsequently solidifying and thus halting the casting operation. It would be accordingly desirable to form dies of the type under consideration in two parts without the above described drawbacks since such would enable not only simplified cavity machining techniques, but would also enable the formation of cavities having square cross-sectional configurations, which configuration in the resultant metal stock would enable it to be more easily reformed into other forms, i.e., sheets, rods etc.